A laser-assisted wafer debonding is used during a semiconductor device manufacturing process. In order to avoid damages on sensitive circuits formed in a wafer, a scan laser beam (i.e., a scanning laser beam or a scanned laser beam) provided by a laser scanning system should be precisely projected on desired locations on a wafer. However, precise alignment of the scan laser beam to the wafer is challenging since a laser scan pattern may vary due to changes in spot size and position of a laser beam on a wafer, and a scan magnification of a laser scanning system. Thus, a method for sensing and calibrating the spot size and position of the laser beam and the scan magnification of the laser scanning system is needed.